The proposed project will examine input-output relationships in the speech of young children with specific speech-language impairment (SSLI). The aim is to provide information concerning the intermediaries between the assumed characteristics of adult speech and the child's production. Such information is not available and is consequently not taken into account either in the description of speech-language impairments or in the design of intervention procedures. The information is particularly important in light of suggested relationships between perceptual abilities and the nature of speech and language development. The proposed research will include six related sets of experiments: (1) discrimination of phonemic contrasts; (2) discrimination of subphonemic, acoustic features; (3) lexical recognition; (4) relationship among the adult production, the child's perception, and the child's production; (5) the relationship between perception and phonological changes in production resulting from intervention; and (6) the development and evaluation of computer-implemented models of these relationships using massively connected, parallel architectures. The subject will be normally developing children, 14 to 24 months of age, and children with SSLI, 30 to 48 months, with production vocabularies of under 50 words who have not yet begun to produce productive two-word utterances. The normal children are an important control because of their comparable linguistic level, their comparable articulation abilities, and the potential effect of their lower chronological age (and normal developmental status) on child-directed adult speech. The project brings several new experimental approaches to bear on these areas. Throughout the research, experimentally contrived words and unfamiliar referents will be used to achieve adequate experimental control. The use of an experimentally controlled procedure for sampling child-directed adult speech will add to observational data currently available. Children's phonological perception and lexical recognition will be examined at an earlier developmental level than has been previously possible using adaptations of bimodal perception procedures. Finally, models will be developed and evaluated using data collected in the course of the project and will be used to further explore potential input, perception, and production relationships.